1. Field of the Invention
The present invention relates to a method of manufacturing a solid-state image sensor.
2. Description of the Related Art
A method of independently exposing a plurality of divided regions using a plurality of photomasks (reticles) so as to form a pattern of one layer is known. Such method will be referred to as dividing exposure hereinafter. Also a method of exposing one region using one photomask so as to form a pattern of one layer is known. Such method will be referred to as non-dividing exposure hereinafter. Note that the concept of “layer” includes a wiring layer such as a polysilicon wiring layer and metal wiring layer arranged on a semiconductor substrate, and also a layer in a semiconductor substrate, which is configured by a two-dimensional array of impurity regions that can be formed by ion implantation into the substrate.
Japanese Patent Laid-Open No. 5-6849 discloses a method of forming, by dividing exposure, a photoelectric conversion device having a size equal to or larger than a field size of a stepper. Japanese Patent Laid-Open No. 2004-111866 discloses a method of forming, through non-dividing exposure, a layer which substantially influences an operation of a semiconductor device and its underlying layers, and forming, through dividing exposure, layers above the layer which substantially influences the operation of the semiconductor device.
In general, an exposure apparatus which can expose a broad region has a lower resolution and alignment precision than those which can expose a narrow region. When a solid-state image sensor has a large imaging region, if that region is formed by non-dividing exposure, an exposure apparatus having a lower resolution and alignment precision has to be used. However, in this case, the number of pixels may be limited or image quality may be limited depending on the resolution of that exposure apparatus. Hence, a solid-state image sensor has to be manufactured by applying dividing exposure. However, when all layers are to be formed by dividing exposure, cost of photomasks, that of a lithography process, and that of the exposure apparatus increase.
Note that the method disclosed by Japanese Patent Laid-Open No. 2004-111866 is based on the idea that a layer which requires a higher resolution and alignment precision and its underlying layers are to be formed by non-dividing exposure. It is difficult for this method to manufacture a large solid-state image sensor having a higher resolution and image quality.